Bioethanol production in batch mode by a native strain of <Emphasis Type="Italic">Zymomonas mobilis</Emphasis>

Two wild strains of Zymomonas mobilis were isolated (named as ML1 and ML2) from sugar cane molasses obtained from different farms of Santander, Colombia. Initially, selection of the best ethanol-producer strains was carried out using ethanol production parameters obtained with a commercial strain Z. mobilis DSM 3580. Three isolated strains were cultivated in a culture medium containing yeast extract, peptone, glucose and salts, at pH 6 and 32°C with stirring rate of 65 rpm during 62 h. The best results of ethanol production were obtained with the native strain ML1, reaching a maximum ethanol concentration of 79.78 g l⁻¹. ML1 and ML2 strains were identified as Z. mobilis, according to the morphology, biochemical tests and molecular characterization by PCR of specific DNA sequences from Z. mobilis. Subsequently, the effect of different nitrogen sources on production of ethanol was evaluated. The best results were obtained using urea at a 0.73 g/l. In this case, maximum concentration of ethanol was 83.81 g l⁻¹, with kinetic parameters of yield of ethanol on biomass (Y_P/X) = 69.01(g g⁻¹), maximum volumetric productivity of ethanol (Qp_max) = 2.28 (g l⁻¹ h⁻¹), specific productivity of ethanol (q_P) = 3.54 (h⁻¹) and specific growth rate (μ) = 0.12 h⁻¹. Finally, we studied the effect of different culture conditions (pH, temperature, stirring, C/N ratio) with a Placket-Burman′s experimental design. This optimization indicated that the most significant variables were temperature and stirring. In the best culture conditions a significant increase in all variables of response was achieved, reaching a maximum ethanol concentration of 93.55 g l⁻¹.     

Heat shock response in psychrophilic and psychrotrophic yeast from Antarctica

The response to heat stress in six yeast species isolated from Antarctica was examined. The yeast were classified into two groups: one psychrophilic, with a maximum growth temperature of 20°C, and the other psychrotrophic, capable of growth at temperatures above 20°C. In addition to species-specific heat shock protein (hsp) profiles, a heat shock (15°C–25°C for 3 h) induced the synthesis of a 110-kDa protein common to the psychrophiles, Mrakia stokesii, M. frigida, and M. gelida, but not evident in Leucosporidium antarcticum. Immunoblot analyses revealed heat shock inducible proteins (hsps) corresponding to hsps 70 and 90. Interestingly, no proteins corresponding to hsps 60 and 104 were observed in any of the psychrophilic species examined. In the psychrotrophic yeast, Leucosporidium fellii and L. scottii, in addition to the presence of hsps 70 and 90, a protein corresponding to hsp 104 was observed. In psychrotrophic yeast, as observed in psychrophilic yeast, the absence of a protein corresponding to hsp 60 was noted. Relatively high endogenous levels of trehalose which were elevated upon a heat shock were exhibited by all species. A 10 Celsius degree increase in temperature above the growth temperature (15°C) of psychrophiles and psychrotrophs was optimal for heat shock induced thermotolerance. On the other hand, in psychrotrophic yeast grown at 25°C, only a 5 Celsius degree increase in temperature was necessary for heat shock induced thermotolerance. Induced thermotolerance in all yeast species was coincident with hsp synthesis and trehalose accumulation. It was concluded that psychrophilic and psychrotrophic yeast, although exhibiting a stress response similar to mesophilic Saccharomyces cerevisiae, nevertheless had distinctive stress protein profiles. Received: August 7, 1997 / Accepted: October 22, 1997     

Gene cloning, expression and characterization of an α-galactosidase from Pedobacter nyackensis MJ11 CGMCC 2503 with potential as an aquatic feed additive

A gene, aga-MJ11, encoding an α-galactosidase (EC 3.2.1.22) was cloned from Pedobacter nyackensis MJ11 CGMCC 2503, expressed in Escherichia coli, and biochemically characterized. The gene consisted of 2,163 nucleotides encoding a 720 amino acid–protein with a theoretical molecular weight of 82.6 kDa. The deduced amino acid sequence of Aga-MJ11 shared the highest identity of 51% to an α-galactosidase from Parabacteroides distasonis (YP_001301506), which belongs to glycoside hydrolase (GH) family 36. Purified recombinant Aga-MJ11-H showed optimal activity at pH 5.5 and 40°C, was stable at pH 4.0–10.0, retained ~80% of the maximum activity at 30°C (the optimum temperature for freshwater fish), exhibited tolerance to some proteases, and had a wide substrate specificity (pNPG, melidiose, stachyose and raffinose). All these features make Aga-MJ11 potentially useful for applications in aquaculture. The enzyme studied in the present work may represent a novel GH-36 α-galactosidase from the genus Pedobacter. X. Liu and K. Meng contributed equally to this work.     

Diversity and enzyme properties of protease-producing bacteria isolated from sub-Antarctic sediments of Isla de Los Estados, Argentina

Protease-producing bacteria isolated from sub-Antarctic marine sediments of Isla de Los Estados (Argentina) were characterized, and the thermal inactivation kinetics of their extracellular proteases compared. Isolates were affiliated with the genera Pseudoalteromonas, Shewanella, Colwellia, Planococcus, and a strain to the family Flavobacteriaceae. Colwellia strains were moderate psychrophiles (optimal growth at about 15°C, maximum growth temperature at around 25°C). 16S rRNA phylogenetic analysis revealed that these strains and Colwellia aestuarii form a distinct lineage within the genus. The remaining isolates were psychrotolerant and grew optimally between 20 and 25°C; two of them represent potentially novel species or genus (16S rRNA < 97% sequence similarity). The thermostability of the extracellular proteases produced by the isolates was analysed, and the inactivation rate constant (k _in), the activation energy (Ea_in) and the activation Gibbs free energy of thermal inactivation (ΔG ^* _in) determined. ΔG ^* _in, calculated at 30°C, varied between 97 and 124 kJ/mol. Colwellia enzyme extracts presented the highest thermosensitivity, while the most thermostable protease activity was shown by Shewanella spp. These results demonstrated that the stability to temperature of these enzymes varies considerably among the isolates, suggesting important variations in the thermal properties of the proteases that can coexist in this environment.     

Chemosensitization of Aflatoxigenic Fungi to Antimycin A and Strobilurin Using Salicylaldehyde,a Volatile Natural Compound Targeting Cellular Antioxidation System

Various species of fungi in the genus Aspergillus are the most common causative agents of invasive aspergillosis and/or producers of hepato-carcinogenic mycotoxins. Salicylaldehyde (SA), a volatile natural compound, exhibited potent antifungal and anti-mycotoxigenic activities to A. flavus and A. parasiticus. By exposure to the volatilized SA, the growth of A. parasiticus was inhibited up to 10–75% at 9.5 mM ≤ SA ≤ 16.0 mM, while complete growth inhibition was achieved at 19.0 mM ≤ SA. Similar trends were also observed with A. flavus. The aflatoxin production, i.e., aflatoxin B₁ and B₂ (AFB₁, AFB₂) for A. flavus and AFB₁, AFB₂, AFG₁, and AFG₂ for A. parasiticus, in the SA-treated (9.5 mM) fungi was reduced by ~13–45% compared with the untreated control. Using gene deletion mutants of the model yeast Saccharomyces cerevisiae, we identified the fungal antioxidation system as the molecular target of SA, where sod1Δ [cytosolic superoxide dismutase (SOD)], sod2Δ (mitochondrial SOD), and glr1Δ (glutathione reductase) mutants showed increased sensitivity to this compound. Also sensitive was the gene deletion mutant, vph2Δ, for the vacuolar ATPase assembly protein, suggesting vacuolar detoxification plays an important role for fungal tolerance to SA. In chemosensitization experiments, co-application of SA with either antimycin A or strobilurin (inhibitors of mitochondrial respiration) resulted in complete growth inhibition of Aspergillus at much lower dose treatment of either agent, alone. Therefore, SA can enhance antifungal activity of commercial antifungal agents required to achieve effective control. SA is a potent antifungal and anti-aflatoxigenic volatile that may have some practical application as a fumigant.     

Growth, lipid accumulation, and fatty acid composition in obligate psychrophilic, facultative psychrophilic, and mesophilic yeasts

Obligate psychrophilic, facultative psychrophilic, and mesophilic yeasts were cultured in a carbon-rich medium at different temperatures to investigate whether growth parameters, lipid accumulation, and fatty acid (FA) composition were adaptive and/or acclimatory responses. Acclimation of facultative psychrophiles and mesophiles to a lower temperature decreased their specific growth rate, but did not affect their biomass yield (Y_X/S). Obligate and facultative psychrophiles exhibited the highest Y_X/S. Acclimation to lower temperature decreased the lipid yield (Y_L/X) in mesophilic yeasts, but did not affect Y_L/X in facultative psychrophilic ones. Similar Y_L/X were found in both groups of psychrophiles, suggesting that lipid accumulation is not a distinctive characteristic of adaptation to permanently cold environments. The unsaturation of FAs was one major adaptive feature of the yeasts colonizing permanently cold ecosystems. Remarkable amounts of α-linolenic acid were found in obligate psychrophiles at the expense of linoleic acid, whereas it was scarce or absent in all the other strains. Increased unsaturation of FAs was also a general acclimatory response of facultative psychrophiles to a lower temperature. These results improve the knowledge of the responses enabling psychrophilic yeasts to cope with the cold and may be of support for potential biotechnological exploitation of these strains.     

Dimensionless analysis of the microbial growth rate dependence on sub-optimal temperatures

The influence of sub-optimal temperatures (T) on the microbial growth rate (μ) has been assessed by means of dimensionless variables: T_dim = [T−T_min]/[T_opt−T_min] and μ_dim = μ/μ_opt. T_min represents the temperature at which there is no growth, T_opt the optimum temperature at which the growth rate, μ_opt, is maximum. Data sets, growth rate vs temperature, have been taken from the literature for 12 organisms (psychrotrophs, mesophiles and thermophiles). In order to compare these organisms, the power law function has been used: [μ_dim] = [T_dim]^α. The parameters μ_opt and T_opt are determined from direct readings whereas T_min and αare estimated by means of a non-linear regression. An accurate estimation of T_min is obtained providing low growth rate data are available. A wide range of optimal temperatures where the growth rate almost equals μ_opt prevents one from obtaining a narrow confidence interval forα. On the basis of the analysis hereafter developed, thermophiles are characterized by values of the power α less than mesophiles and psychrotrophs. Almost all of these values are significantly different from two, previously determined for Staphylococcus xylosus and widely used for predicting the microbial growth in foods. Received 15 May 1998/ Accepted in revised form 25 September 1998     

Photosynthetic characteristics and physiological plasticity of an Aphanizomenon flos-aquae (Cyanobacteria, Nostocaceae) winter bloom in a deep oligo-mesotrophic lake (Lake Stechlin, Germany)

In winter of 2009/2010, Aphanizomenon flos-aquae bloomed in the ice and snow covered oligo-mesotrophic Lake Stechlin, Germany. The photosynthesis of the natural population was measured at eight temperatures in the range of 2–35°C, at nine different irradiance levels in the range of 0–1,320 μmol m⁻² s⁻¹ PAR at each applied temperature. The photoadaptation parameter (I _k) and the maximum photosynthetic rate (P _max) correlated positively with the temperature between 2 and 30°C, and there was a remarkable drop in both parameters at 35°C. The low I _k at low temperatures enabled the active photosynthesis of overwintering populations at low irradiance levels under ice and snow cover. The optimum of the photosynthesis was above 20°C at irradiances above 150 μmol m⁻² s⁻¹. At lower irradiance levels (7.5–30 μmol m⁻² s⁻¹), the photosynthesis was the most intensive in the temperature range of 2–5°C. The interaction between light and temperature allowed the proliferation of A. flos-aquae in Lake Stechlin resulting in winter water bloom in this oligo-mesotrophic lake. The applied 2°C is the lowest experimental temperature ever in the photosynthesis/growth studies of A. flos-aquae, and the results of the P–I and P–T measurements provide novel information about the tolerance and physiological plasticity of this species.     

Direct ethanol production from cellulosic materials at high temperature using the thermotolerant yeast Kluyveromyces marxianus displaying cellulolytic enzymes

To exploit cellulosic materials for fuel ethanol production, a microorganism capable of high temperature and simultaneous saccharification–fermentation has been required. However, a major drawback is the optimum temperature for the saccharification and fermentation. Most ethanol-fermenting microbes have an optimum temperature for ethanol fermentation ranging between 28 °C and 37 °C, while the activity of cellulolytic enzymes is highest at around 50 °C and significantly decreases with a decrease in temperature. Therefore, in the present study, a thermotolerant yeast, Kluyveromyces marxianus, which has high growth and fermentation at elevated temperatures, was used as a producer of ethanol from cellulose. The strain was genetically engineered to display Trichoderma reesei endoglucanase and Aspergillus aculeatus β-glucosidase on the cell surface, which successfully converts a cellulosic β-glucan to ethanol directly at 48 °C with a yield of 4.24 g/l from 10 g/l within 12 h. The yield (in grams of ethanol produced per gram of β-glucan consumed) was 0.47 g/g, which corresponds to 92.2% of the theoretical yield. This indicates that high-temperature cellulose fermentation to ethanol can be efficiently accomplished using a recombinant K. marxianus strain displaying thermostable cellulolytic enzymes on the cell surface.     

Effects of physical culture parameters on bacteriocin production by Mexican strains of Bacillus thuringiensis after cellular induction

We have shown previously that in the presence of inducer Bacillus cereus 183, significant increases in bacteriocin production and bactericidal activity of B. thuringiensis occur when the latter is cultivated at pH 7.2, 28°C, and 180 rpm. Here we show that this activity can be further improved when B. thuringiensis is induced with B. cereus 183 and then cultivated with modification of pH, temperature, and agitation. Five native strains of B. thuringiensis, LBIT 269, LBIT 287, LBIT 404, LBIT 420, and LBIT 524 which synthesize, respectively, morricin 269, kurstacin 287, kenyacin 404, entomocin 420, and tolworthcin 524, were cultivated in four different fermentation media. Of these, fermentation in tryptic soy broth (TSB) yielded the highest level of bacteriocin activity (~100–133 FU). Bacteria grown in TSB were induced with B. cereus 183 and cultivated at different pH (6.0, 7.2, 8.0), temperature (26, 28, 30°C), and agitation (150, 180, 210 rpm). Full factorial design was performed and results were analyzed with analysis of variance (ANOVA) and Tukey multiple comparison tests at significant level of α ≤ 0.05 to study the influence of the three variables on bacterial growth and bacteriocin production. Our data show that the highest bacteriocin activity was found with LBIT 269 and LBIT 404 with an increase of ~95–100% compared with induced B. thuringiensis strains cultivated under fixed conditions (pH 7.2, 28°C, 180 rpm), for which the data were set at 0%. The optimal conditions for morricin 269 and kenyacin 404 production were, respectively, pH 8, 30°C, 210 rpm and pH 7.2, 26°C, 210 rpm.     

Development of a semidefined growth medium for Pedobacter cryoconitis BG5 using statistical experimental design

Pedobacter cryoconitis BG5 are psychrophiles isolated from the cold environment and capable of proliferating and growing well at low temperature regime. Their cellular products have found a broad spectrum of applications, including in food, medicine, and bioremediation. Therefore, it is imperative to develop a high-cell density cultivation strategy coupled with optimized growth medium for P. cryoconitis BG5. To date, there has been no published report on the design and optimization of growth medium for P. cryoconitis, hence the objective of this research project. A preliminary screening of four commercially available media, namely tryptic soy broth, R2A, Luria Bertani broth, and nutrient broth, was conducted to formulate the basal medium. Based on the preliminary screening, tryptone, glucose, NaCl, and K₂HPO₄ along with three additional nutrients (yeast extract, MgSO₄, and NH₄Cl) were identified to form the basal medium which was further analyzed by Plackett–Burman experimental design. Central composite experimental design using response surface methodology was adopted to optimize tryptone, yeast extract, and NH₄Cl concentrations in the formulated growth medium. Statistical data analysis showed a high regression factor of 0.84 with a predicted optimum optical (600?nm) cell density of 7.5 using 23.7?g/L of tryptone, 8.8?g/L of yeast extract, and 0.7?g/L of NH₄Cl. The optimized medium for P. cryoconitis BG5 was tested, and the observed optical density was 7.8. The cost-effectiveness of the optimized medium was determined as 6.25 unit prices per gram of cell produced in a 250-ml Erlenmeyer flask.     

Physiological diversity within the <Emphasis Type="Italic">kluyveromyces marxianus</Emphasis> species

The Kluyveromyces marxianus strains CBS 6556, CBS 397 and CBS 712^T were cultivated on a defined medium with either glucose, lactose or sucrose as the sole carbon source, at 30 and 37°C. The aim of this work was to evaluate the diversity within this species, in terms of the macroscopic physiology. The main properties evaluated were: intensity of the Crabtree effect, specific growth rate, biomass yield on substrate, metabolite excretion and protein secretion capacity, inferred by measuring extracellular inulinase activity. The strain Kluyveromyces lactis CBS 2359 was evaluated in parallel, since it is the best described Kluyveromyces yeast and thus can be used as a control for the experimental setup. K. marxianus CBS 6556 presented the highest specific growth rate (0.70 h⁻¹) and the highest specific inulinase activity (1.65 U mg⁻¹ dry cell weight) among all strains investigated, when grown at 37°C with sucrose as the sole carbon source. The lowest metabolite formation and highest biomass yield on substrate (0.59 g dry cell weight g sucrose⁻¹) was achieved by K. marxianus CBS 712^T at 37°C. Taken together, the results show a systematic comparison of carbon and energy metabolism among three of the best known K. marxianus strains, in parallel to K. lactis CBS 2359.     

Isolation and characterization of eight microsatellite loci from the endangered plant species Hypochaeris salzmanniana (Asteraceae)

We report the isolation and characterization of eight microsatellite loci for Hypochaeris salzmanniana, an endangered species endemic to the southwestern coast of Spain and the Atlantic coast of Morocco. A total of 32 alleles were detected across a sample of 45 individuals, with an average number of 4.0 alleles per locus. The average polymorphic information content (PIC) was 0.533 and the observed (H _O) and expected (H _E) heterozygosity values varied from 0.022 to 0.978 and from 0.434 to 0.759, respectively. Five loci exhibited significant deviation from Hardy–Weinberg equilibrium (P ≤ 0.001) and three pairs of loci showed significant linkage disequilibrium (P ≤ 0.01). The eight loci were tested for transferability in three others species (H. arachnoidea, H. glabra, and H. radicata) belonging to the same section of H. salzmanniana. With the exception of locus Hsalz7, all loci successfully amplified in the three species. These preliminary data confirm the usefulness of microsatellite markers for assessing the ecology and genetic structure of H. salzmanniana and to understand the evolution of species within the section Hypochaeris.     

Yeast cultivation in lettuce brine

The use of lettuce brine, a by-product of the vegetable fermentation industry, as a medium for yeast cultivation was investigated. Six strains of yeast, Saccharomyces sp., Pichia sp., Rhodotorula sp., Candida sp., Kluyveromyces sp. and Trichospora sp. grew well in diluted lettuce brine under aerobic conditions. The acid brine becomes neutral after yeast cultivation. The yeast strains reached the maximum growth after the first day of cultivation. Trichosporon sp. was found to grow best in the brine with the maximum specific growth rate at 0.09 h⁻¹ and growth yield of 67%. This revised version was published online in November 2006 with corrections to the Cover Date.     

Hydrocarbon degradation and enzyme activities of cold-adapted bacteria and yeasts

The potential of 89 culturable cold-adapted isolates from uncontaminated habitats, including 61 bacterial and 28 yeast strains, to utilize representative fractions of petroleum hydrocarbons (n-alkanes, monoaromatic and polycyclic aromatic hydrocarbons) for growth and to produce various enzymes at 10°C was investigated. The efficiency of bacterial and yeast strains was compared. The growth temperature range of the yeast strains was significantly smaller than that of the bacterial strains. Sixty percent of the yeasts but only 8% of the bacteria could be classified as true psychrophiles, showing no growth above 20°C. A high percentage (89%) of the yeast strains showed lipase activity. More than one-third of the 61 bacterial strains produced amylase, -lactamase, -galactosidase or lipase; more than two-thirds were protease producers. Only 6% of the bacterial strains but 79% of the yeast strains utilized n-hexadecane for growth; 13% of the bacterial strains and 21–32% of the yeast strains utilized phenol, phenanthrene or anthracene for growth. Only four yeast strains but none of the bacterial strains could grow with all hydrocarbons tested. The biodegradation of phenol was investigated in fed-batch cultures at 10°C. Three yeast strains degraded phenol concentrations as high as 10 mm (one strain) or 12.5 mm (two strains). Of eight bacterial strains, two strains degraded up to 10 mm phenol. The optimum temperature for phenol degradation was 20°C for all eight bacterial strains and for two yeast strains. Biodegradation by five yeast strains was optimal at 10°C and faster at 1°C than at 20°C. All phenol-degrading strains produced catechol 1,2 dioxygenase activity.Communicated by K. Horikoshi     

Morphometry and growth of three <Emphasis Type="Italic">Synechococcus</Emphasis>-like picoplanktic cyanobacteria at different culture conditions

Three phycocyanin-rich strains of Synechococcus-like picoplanktic cyanobacteria, isolated from the plankton of Czech oligotrophic to eutrophic freshwater reservoirs, were investigated in crossed gradients of light and temperature and in combination with two different culture media (BG-11 and WC). The strains exhibited similar growth and reproduction patterns and displayed overlapping ranges of cell size (1.5 × 0.8 μm) under standardized laboratory conditions (18 μmol m⁻² s⁻¹; 20°C). However, strains behavior differed in the crossed gradients. All strains preferred BG-11 medium, where also remarkable size changes could be observed. Length, width, cell abundance and growth rate of two strains were positively correlated with temperature and nutrients, whereas the impact of light intensity was insignificant. Maximum cell elongation (involution cells up to 19 μm) occurred in two strains only in BG-11 medium at highest temperature (28°C) and highest irradiance (53 μmol m⁻² s⁻¹). Cell dimensions in WC medium were constant under most conditions given. The third strain was influenced by all three factors, from which light and nutrients played pivotal role. The length of the lag-phase for all strains appeared to be temperature dependent (negative correlation). Despite the fact that the cell volume in all strains increased more than five times under the lowest light and low temperature (6 μmol m⁻² s⁻¹, <15°C) in both media, the length/width ratio remained unchanged. The strains differed in the degree of cell enlargement and cell division symmetry as well as in optimum temperature and light dependence. Based on this experimental work two strains could be identified as Synechococcus sp. and one as Cyanobium sp., which can be used as a support for the following genetical analyses.     

Growth Temperatures and Temperature Characteristics of Aeromonas

Six of the 13 Aeromonas hydrophila, 1 of 10 A. shigelloides, and none of 10 A. salmonicida were found to be psychrophiles. All of the rest of the strains were mesophiles. The mu values (temperature characteristics) could not be used to distinguish psychrophiles from mesophiles.     

Effects of temperature and light on the growth and geosmin production of Lyngbya kuetzingii (Cyanophyta)

The effects of temperature and light on the growth and geosmin production of Lyngbya kuetzingii were determined. Of the three temperatures tested, 10, 25 and 35°C, the maximal geosmin concentration and geosmin productivity were yielded at 10°C, while the highest chl a production was observed at 25°C. In the studies on light intensity, the maximal geosmin concentration and geosmin productivity were observed at 10 μmol m⁻² s⁻¹, while the highest chl a production was at 20 μmol m⁻² s⁻¹. It was suggested that more geosmin was synthesized with lower chl a demand. Meanwhile, the relative amounts of extra- and intracellular geosmin were investigated. Under optimum growth conditions (20 μmol m⁻² s⁻¹, 25°C; BG-11 medium), the amounts of extracellular geosmin increased as the growth progressed and reached the maximum in the stationary phase, while the intracellular geosmin reached its maximum value in the late exponential phase, and then began to decline. However, under the low temperature (10°C) or light (10 μmol m⁻² s⁻¹) conditions, more intracellular geosmin was synthesized and mainly accumulated in the cells. The proportions of extracellular geosmin were high, to 33.33 and 32.27%, respectively, during the stationary phase at 35°C and 20 μmol m⁻² s⁻¹. It was indicated that low temperature or light could stimulate geosmin production and favor the accumulation of geosmin in cells, while more intracellular geosmin may be released into the medium at higher temperatures or optimum light intensity.     

Life cycle,population dynamics,growth and production of <Emphasis Type="Italic">Abra segmentum</Emphasis> (Mollusca,Bivalvia) at low salinities in a Mediterranean lagoon

Aspects of the biology of Abra segmentum were investigated at low salinities in a Mediterranean coastal lagoon (Monolimni Lagoon, Northern Aegean Sea). Monthly samples were collected during the period from February 1998 to January 1999. Recruitment occurred from mid-spring to early autumn (0.3–5.7 psu) and recruits grew during summer and autumn (1.2–5.7 psu), while a major part vanished during next autumn, displaying a maximum life span of about 20 months. A positive correlation was found between the percentage of individuals having a shell length of ≤3.5 mm and temperature; age group 0 showed a growth rate of 0.97 mm per month, and the largest individual collected had a 19.76 mm shell length. The population density sharply increased during late spring (0.3–1.2 psu); this increase was followed by a decline during summer and, afterwards, a gradual increase up to late autumn. Secondary production calculated by the size–frequency method gave a mean annual density (n) of 3,357 individuals m⁻², a mean annual biomass (B) of 21.98 g DW m⁻², an annual production (P) of 73.72 g DW m⁻² and a P:B ratio of 3.35. A comparison of the present data with available data of A. segmentum populations from higher salinity habitats revealed that this bivalve in the study area showed a life history pattern similar to that of other populations of the species and a comparatively high growth rate, maximum body size, n, B, P and P:B ratio. Our findings suggest that the studied aspects of A. segmentum biology could not be markedly affected by low salinities.     

Growth and photosynthetic characteristics of several <Emphasis Type="Italic">Cosmarium</Emphasis> strains (Zygnematophyceae,Streptophyta) isolated from various geographic regions under a constant light-temperature regime

Numerous detailed studies have been made of climatically and environmentally influenced macroalgal geographic distribution patterns. However, so far, there have been only a few intrinsic investigations of the geographic distributions of microalgae. In order to investigate the physiological differences among geographically different microalgal strains, six Cosmarium strains were collected from various climate areas and studied. They were grown under a constant light-temperature regime (16°C and 30 μmol photons m⁻² s⁻¹) and nutrient supply. The arctic representative, C. crenatum var. boldtianum, and the typical tropical desmid, C. beatum, behaved like algae adapted to high light intensities, as judged from the distinctly high values of photosynthetic capacity and saturating irradiance measured, in accordance with the high solar radiation prevailing in their sampling areas. The arctic taxon appeared more optimally suited to the low cultivation temperature, as evidenced by the relatively high values of growth rates, maximum quantum yield and photosynthetic efficiency measured. The cosmopolitan taxa, C. meneghinii and C. punctulatum var. subpunctulatum, exhibited a high maximum quantum yield and photosynthetic efficiency concomitantly during growth, which explained their ubiquitous distribution. Nevertheless, two clones belonging to C. punctulatum var. subpunctulatum, collected from polar and mountainous tropical regions, differed significantly with regard to cell volume, growth rates, surface area to volume ratio and photosynthetic parameters. The physiological differences between the Cosmarium strains were in accordance with their geographic origin; they are discussed in detail in this study. Moreover, these differences were maintained despite the long-term cultivation under identical and constant laboratory conditions.